Technical Abstract:
The porcine placenta is classified as epitheliochorial with a diffuse distribution of chorionic villi that do not invade maternal tissues. Thus, the maternal and fetal bloodstreams are separated by six distinct tissue layers. The porcine fetal-maternal interface (FMI) is substantially folded to increase the interactive surface area, becomes more folded as gestation advances, and it is likely that the extent of folding plays a significant role in fetal survival. We have reported that the depth folding along the FMI is inversely related to the size of the fetus. We have also shown that the abundance of enzymes known to degrade the fetal extracellular matrix of the placenta increases with advancing gestation and in placentas of small fetuses. Furthermore, we have evidence demonstrating there is differential localization of heparanase (HSPE) gene expression within the fetal maternal interface, which corresponds to phenotypic differences in trophoblast epithelial cells (short cuboidal: SC; tall columnar: TC). We hypothesized that the phenotypically and spatially distinct trophoblast epithelial cells differ in their contribution to fold development, differing in their capacity for cell migration and that these differences would be reflected in their transcriptome. Populations of phenotypically distinct SC and TC trophoblast epithelial cells were isolated from day 85 ± 3 cross-sections of porcine placentas (n = 4) using laser capture microdissection. RNA-seq was performed on an Illumina Hi-seq 2000 and reads were mapped to the Sus Scrofa genome (v 9.2). Expression was conveyed using the RPKM method and 7398 unique genes/sequences met the minimum expression threshold (1.8 RPKM). Expression data was analyzed by one-way ANOVA with adaptive false discovery rate via JMP Genomics (v 5.0) and differences were considered statistically significant when P </= 0.05. Functional analysis of genes with at least moderate abundance (RPKM 20) was generated through the use of Ingenuity Pathway Analysis. Pathway analysis of the gene expression from the two cell types indicates that both cell types express genes known to be associated with the IPA annotated pathway Invasion of Cells and that the SC cells are predicted to be more invasive than TC cells (Z score of 2.278). Of the 116 genes in this dataset known to be involved in cell invasion, 44 (including HPSE) were found to have differential abundance between the two cell types (P </= 0.05). These data establish that trophoblast epithelial cells of the pig placenta possess a transcriptome consistent with an invasive cell type. As the porcine placenta does not invade maternal tissue, these genes are likely to be involved in fold development; future experiments investigating how nutritional or genetic factors influence folding of the FMI may help to improve the development or function of the porcine placenta.
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